Variability of G(2) checkpoint sensitivity to low doses of X-rays (2 cGy): correlation with G(2) chromatid aberrations but not with an adaptive response.

Using human lymphocytes from a group of 20 donors, we investigated (i) the X-ray-induced adaptive response (AR) after four different conditioning treatments of 1, 2, 4 and 6 cGy, (ii) chromosomal sensitivity to X-irradiation during G(2) and (iii) the G(2)/M checkpoint response. An AR was found in 11 of the 18 donors (approximately 60%). No correlation was found between the presence of AR and G(2) chromosomal radiosensitivity, or with donor sensitivity to the activation of the G(2)/M checkpoint by 30 cGy or a dose as low as 2 cGy. The AR was not related to any particular conditioning treatment, but was consistently present or absent in any one donor under all conditioning treatments used. As far as chromosomal breakage and induced mitotic delay in G(2) are concerned, large variability between individuals was observed, together with a close correlation in the same donor between mitotic delay induced by a low dose (2 cGy) and the frequency of aberrations.